Reactive Redis does not continually publish changes to the Flux - spring-boot

Question

I am trying to get live updates on my redis ordered list without success.
It seems like it fetches all the items and just ends on the last item.
I would like the client to keep get updates upon a new order in my ordered list.
What am I missing?
This is my code:
#RestController
class LiveOrderController {
#Autowired
lateinit var redisOperations: ReactiveRedisOperations<String, LiveOrder>
#GetMapping(produces = [MediaType.TEXT_EVENT_STREAM_VALUE], value = "/orders")
fun getLiveOrders(): Flux<LiveOrder> {
val zops = redisOperations?.opsForZSet()
return zops?.rangeByScore("orders", Range.unbounded())
}
}

Answer 1

There is no such feature in Redis. First, reactive retrieval of a sorted set is just getting a snapshot, but your calls are going in a reactive fashion. So you need a subscription instead.
If you opt in for keyspace notifications like this (K - enable keyspace notifications, z - include zset commands) :
config set notify-keyspace-events Kz
And subscribe to them in your service like this:
ReactiveRedisMessageListenerContainer reactiveRedisMessages;
// ...
reactiveRedisMessages.receive(new PatternTopic("__keyspace#0__:orders"))
.map(m -> {
System.out.println(m);
return m;
})
<further processing>
You would see messages like this: PatternMessage{channel=__keyspace#0__:orders, pattern=__keyspace#0__:orders, message=zadd}. It will notify you that something has been added. And you can react on this somehow - get the full set again, or only some part (head/tail). You might even remember the previous set, get the new one and send the diff.
But what I would really suggest is rearchitecting the flow in some way to use Redis Pub/Sub functionality directly. For example: publisher service instead of directly calling zadd will call eval, which will issue 2 commands: zadd orders 1 x and publish orders "1:x" (any custom message you want, maybe JSON).
Then in your code you will subscribe to your custom topic like this:
return reactiveRedisMessages.receive(new PatternTopic("orders"))
.map(LiveOrder::fromNotification);